docs: def addChromosome(
              self, chrom, tax_id, tax_label=None, build_id=None, build_label=None):
          """
          if it's just the chromosome, add it as an instance of a SO:chromosome,
          and add it to the genome. If a build is included,
          punn the chromosome as a subclass of SO:chromsome, and make the
          build-specific chromosome an instance of the supplied chr.
          The chr then becomes part of the build or genome.
          """
          family = Family(self.graph)
          # first, make the chromosome class, at the taxon level
          chr_id = makeChromID(str(chrom), tax_id)
          if tax_label is not None:
              chr_label = makeChromLabel(chrom, tax_label)
          else:
              chr_label = makeChromLabel(chrom)
          genome_id = self.makeGenomeID(tax_id)
          self.model.addClassToGraph(chr_id, chr_label, self.globaltt['chromosome'])
          self.addTaxon(tax_id, genome_id)  # add the taxon to the genome
  
          if build_id is not None:
              # the build-specific chromosome
              chrinbuild_id = makeChromID(chrom, build_id)
              if build_label is None:
                  build_label = build_id
              chrinbuild_label = makeChromLabel(chrom, build_label)
              # add the build-specific chromosome as an instance of the chr class
  
              self.model.addIndividualToGraph(chrinbuild_id, chrinbuild_label, chr_id)
  
              # add the build-specific chromosome
              # as a member of the build (both ways)
              family.addMember(build_id, chrinbuild_id)
              family.addMemberOf(chrinbuild_id, build_id)
  
          return